Fears that Russia could claw back a second chunk of former Soviet territory in Europe grew on Sunday after NATO warned that Moscow’s troops were poised to move into a pro-Russian enclave of Moldova.

NATO’s top commander said that Russian troops massed on Ukraine’s eastern border were well placed to take Transdniester, a Russian-speaking enclave that has declared independence from the rest of Moldova.

About a third of Transdniester’s half-million people are ethnic Russians, many of whom want to return to rule from Moscow. To this day, the streets of the capital, Tiraspol, are decked out with statues of Lenin and other symbols of the Soviet Union, of which Moldova was a member until its break-up in 1991.

U.S. Air Force General Philip Breedlove, who is NATO’s supreme allied commander in Europe, said that gave President Vladimir Putin a pretext to send troops in there as a “protection” force for ethnic Russians, just as he has done in Crimea.

“There is absolutely sufficient [Russian] force postured on the eastern border of Ukraine to run to Transdniester if the decision was made to do that, and that is very worrisome,” he said at a meeting in Brussels hosted by the Marshall Fund, a German think tank.

General Breedlove’s comments came as Ukraine’s new pro-Western government said it feared that Russia planned further military annexations of the east of the country. On Saturday, Russian forces attacked another Ukrainian military base in Crimea, as part of their drive to force Ukrainian troops out the peninsula.

The commander of the base, Colonel Yuli Mamchur, is now in Russian custody, prompting accusations Sunday night from the Ukrainian president, Oleksandr Turchynov, that he had been “abducted.”

Meanwhile, Andriy Parubiy, the head of Ukraine’s national security and defence council, issued a dire warning of the Kremlin threat at a mass rally in the Ukrainian capital, Kiev. “The aim of Putin is not Crimea but all of Ukraine,” he said. “His troops massed at the border are ready to attack at any moment.”

His words were echoed by Tony Blinken, the U.S. deputy national security adviser. He said that, while the Russian troop build-up was probably just for show, “it’s possible that they are preparing to move in.”

Frank-Walter Steinmeier, Germany’s foreign minister, also warned of the huge repercussions of Russia’s attempt to redraw national borders in Europe, describing it as a “Pandora’s Box.”

Russia’s defence ministry boasted yesterday that its flag was now flying over 189 Ukrainian military installations on the Crimean peninsula.

At a Ukrainian base at the Crimean port of Feodosia, marines were negotiating to hand over to Russian forces. “Our only issue is that we want to leave this place with honour, weapons and vehicles,” one Ukrainian soldier said.

Vladimir Chizhov, Moscow’s ambassador to the European Union, insisted that Russia had no intention to move troops outside Crimea, but NATO feels that the Kremlin’s ambitions may go well beyond just Ukraine. An incursion into Transdniester would bring a Russian territorial dispute close to the doorstep of the European Union.

Since it fought a brief separatist war to break away from Moldova in 1991, Transdniester has been home to a “peacekeeping” garrison of about 1,000 Russian troops. Until now, the Kremlin has treated the enclave as being too small to be worth incorporating into the Russian Federation and has officially recognised Transdniester as being part of Moldova. But events in Ukraine may have shifted Moscow’s calculation.

The (Russian) force that is at the Ukrainian border now to the east is very, very sizeable and very, very ready

Recently, the speaker of Transdniester’s parliament urged Russia to incorporate the region. General Breedlove said he suspected that the Kremlin now viewed the enclave as the “next place where Russian-speaking people may need to be incorporated.”

He warned: “The (Russian) force that is at the Ukrainian border now to the east is very, very sizeable and very, very ready.” He did not specify how the Russian forces would get there. Transdniester is landlocked, and a conventional ground operation would require Russian troops to travel through much of western Ukraine. However, Russian forces based in the eastern side of the Black Sea and Crimea might be airlifted.

Moldova, a nation of five million people, is Europe’s poorest.

It has ambitions eventually to become part of the European Union and is currently negotiating a free-trade agreement with Brussels, similar to the one that Ukraine’s now-ousted president, Viktor Yanukovych, abandoned last November under pressure from the Kremlin.

Signing the agreement would take Moldova firmly into the European fold, but Transdniester’s unresolved status would make full membership of the EU or NATO more complicated.

Some analysts believe the Kremlin therefore has a direct vested interest in fomenting trouble in the region.